The invention relates to a solar device in which an air stream is guided through and heated by an absorber of an air receiver that is heated by solar radiation, the heated air stream is cooled by removing useful heat energy, especially by generating steam, and at least a portion of the cooled air stream is returned in a plurality of partial streams to the upstream side of the absorber.
From CH-Z "Technische Rundschau Sulzer" 3/1989, P. 9-14, especially FIG. 10, such a solar device is known in which the not completely cooled air is guided from the steam generator into a warm air chamber upstream of the absorber. From there the air flows through suitable nozzles toward the absorber. It is stated that, for example, 60% of the not completely cooled heated air is returned into the circuit. A similar device is known from EP 399 381 A1 in which the outer edges of the absorber are also surrounded by a warm air chamber. In this arrangement a protective air stream is provided in front of the return air for preventing heat loss, which protective air stream flows to the exterior.
With respect to the technology of an air receiver reference is further made to EP 124 769 B1.
In the known method it is thus desired to return the air cooled by removal of useful heat energy, especially by generating steam, which cooled air still contains a considerable amount of detectable heat, be returned to the receiver substantially completely so that the air sucked through the receiver is preheated. In the known arrangements a warm air channel is arranged about the absorber from which the warm return air is blown toward the surface of the receiver that is radiated by the sun. In the known arrangement it is difficult to distribute the returned warm air corresponding to the radiation intensity profile that is present at the absorber over the entire receiver surface, especially when during operation of the device a strong wind is present and/or the upstream side of the absorber is relatively large. It should be noted that for a solar device having a steam output of 100 MW.sub.th the receiver must have a diameter of approximately 15 m.
It is therefore an object of the present invention to provide a solar device of the aforementioned kind in which a desired distribution of the returned air across the upstream side of the receiver is achieved without substantially affecting the efficiency with respect to the conversion of solar radiation to heat.